Google has announced a $625 million acquisition of Postini, a major provider of corporate communications security and spam filtering services. Postini will become a wholly-owned Google subsidiary when the deal closes at the end of the third quarter. Google is framing the acquisition as part of their Google Apps strategy, pitching Postini as the perfect addition to their Gmail, Calendar, Talk, Docs & Spreadsheets, and Personal Start Page efforts. Google will tap Postini's cadre of services to add security, archiving and policy enforcement to Google Apps.